puppet: Move postgres Nagios plugin to main postgres-common.

This plugins package is required in order to use Nagios checks to
verify the Zulip postgres database, and thus belongs in the default
package set.

puppet/zulip/manifests/postgres_common.pp

@@ -12,6 +12,8 @@ class zulip::postgres_common {
                         "ssl-cert",
                         # our dictionary
                         "hunspell-en-us",
+                        # Postgres Nagios check plugin
+                        "check-postgres",
                         ]
   define safepackage ( $ensure = present ) {
     if !defined(Package[$title]) {

puppet/zulip_ops/manifests/postgres_common.pp

@@ -8,8 +8,6 @@ class zulip_ops::postgres_common {
                                  "python-pip",
                                  # "python3-gevent", # missing on trusty
                                  "python-gevent",
-                                 # Postgres Nagios check plugin
-                                 "check-postgres",
                                  ]
   package { $internal_postgres_packages: ensure => "installed" }